Day 14 - 06/10/14

Question 0

Where do you find Class 2 cells?

Answer 0

Antigen Presenting Cells (APC)
Dendritic Cells
Macrophages
B Cells

Question 1

Where do you find Class 1 cells?

Answer 1

All NUCLEATED cells

Question 2

Which cells are professional antigen presenting cells?

Answer 2

Dendritic Cells
Macrophages
B Cells

Question 3

What are the TWO types of ways ANTIGENS are acquired by APCs?

Answer 3

Endogenous (Class 1)

Exogeneous (Class 2)

Question 4

Where do Class 1 Antigens get presented to?

Answer 4

CD8+ Cytotoxic T Cells

Question 5

Where do Class 2 Antigens get presented to?

Answer 5

CD4+ T Helper Cells

Question 6

How do Class 1 molecules process?

Answer 6

Endogenous antigens are TARGETED for Degradation by the PROTEOSOME by UBIQUITINATION

Question 7

How do Class 1 molecules present ENDOGENEOUS antigens?

Answer 7

1 - Antigens are produced inside cell (Virus DNA)
2 - MHC Class 1 molecules collect PEPTIDES derived from PROTEINS made in the CYTOSOL

3 - Following Trafficking, Class 1 presents antigens on cell surface
4 - Antigens recognises by the CD8+ cytotoxic T Cell which destroys the virally affected cell.

Question 8

What does UBIQUITINATION entail?

Answer 8

During Infection IFNy induces 2 proteosome enzyme subunits
LMP2
LMP7
Which generate PEPTIDES which bind to MHC CLASS 1

Question 10

How are antigen peptides transported (Class 1)?

Answer 10

Along the Endoplasmic Reticulum (ER) the antigen peptides are TRANSPORTED by TAP(Transporter associated with Antigen Processing)

Question 11

How do Class 2 molecules present EXOGENEOUS antigens?

Answer 11

MHC Class 2 bind peptides made from proteins in the intracellular membrane-bound VESICLES. (Macrophages/B Cells)

Such Peptide-MHC Class 2 are recognised by CD4+ HELPER T CELLS which activate B Cells/Macrophages by

• Release of CYTOKINES
• Cell-Cell contact

Question 12

What is the process by which Antigens are uptaked called? (Class 2)

Answer 12

ENDOCYTOSIS

Question 13

What is the Invariant Chain (Ii)?

Answer 13

• Molecule that blocks peptide groove so Class 2 MHC is blocked from binding with ENDOGENEOUS peptides (Class 1)
• Ii-Clip is digested, then MHC Class 2 binds to EXOGENEOUS antigens

Question 14

How do Class 2 molecules present EXOGENEOUS antigens?

Answer 14

1) Bacteria from outside cell enters and infects MACROPHAGES
2) Bacteria enters VESICLE producing PEPTIDE FRAGMENTS
3) Bacteria Fragments bound by MHC CLASS 2 in vesicles
4) Bound peptides are transported to cell surface

Question 15

For full activation, T-Cells require additional signals.

What’s are they called?

Answer 15

Costimulation/Priming

Cytokine Signal

Question 16

What is Costimulation/Priming?

Answer 16

Bidirectional Signalling between cell surface receptor pairs such as

CD80/86 - from APC
CD28 - from T Cell

Question 17

Give an example of Cytokines introduces by APC to stimulate Effector T Cell differentiation

Answer 17

IL-12

Question 18

When does APC give these costimulary and Cytokine signals?

Answer 18

When inflammation is present.

Question 19

What is TCR binding called?

Answer 19

Ligation

Question 20

What does TCR ligation do?

Answer 20

Prevents AUTOIMMUNITY by TOLERANCE

Question 21

How can pathogens evade antigen processing?

Answer 21

1) Enter the CYTOPLASM
e. g. LISTERIA

2) Block PHAGOSOME/LYSOSOME fusion
e. g. M. TUBERCULOSIS

3) Degrade MHC Class II
e. g. LEISHMANIA